Oil burner control



April 2, 1940. l v. H. HARDY 2,195,650

OIL BURNER CONTROL Filed April 14, 1938 2 Sheets-Sheet 2 *LINE l 25 26TRANSFORMEP RELAY WARP SWITCHES 56 5a 57716K SWITCH Snoentor l Pm-siedApr. 2, 1940 UNITED STATES PATENT OFFICE OIL BURNER CONTROL Vaughn H.Hardy, Rochester, N. Y., assignor to General Motors Corporation,Detroit, Mich., a

corporation of Delaware Application April 14, 1938, Serial No. 202,025

8 Claims.

i 5 With the advent of the domestic use of fluid fuel burners such asoil or gas fire furnaces, it has become necessary to provide suitablecontrols for said burners or furnaces which will require ,very little,if any, attention, maintain the heat l at a predetermined set level, andembody certain safety features which will keep the device sufIicientlysafe for home use.

It is therefore an object of my invention to r provide such a system forburner control. il It is a further object to provide a control syste nembodying the necessary safety features to deenergize the whole systemunder certain circumstances, namely, when lthe burner does not initiallystart or where therey is a ame or cur- `2|) rent failure after theburner isoperating normally. n

It is a still further object of my invention to providesuch a controlsystem as will be comv.paratively simple in constructionand easily ap-"25 plied to .an existing heating plant.A K y With these and` otherobjects in view, the. em-

bodiments of my invention will be best understood by'reference to thefollowing specification .and` claims and the illustrations in the accomnpanying drawings, in which:

yl'igure 1 is a circuit diagram of a control sys` tem of my invention.

Figure 2 is also a circuit diagram of a, modiiiedform of my invention;

. a Figure 3 is a circuit diagram of a further modication. l Referringnow more specifically to Figure 1, there is provided an incomingline 2,4 to which the supply such as llOvolts is` provided. There is form ofVstack switch 8, whichfhas a bimetal portionV I0 extending into andsensitive to the heat in the furnace chamber; .a room thermostat I2;

`and a transformer relay I4' having a primary l 5 I6 and a secondary I8,ythe magnetic `field of.

which operates afplurality of switches-20 and l22.v

There is also provided-an ignition transformer 24, thefmain warpswitch`26 which Iincludes a heating coil 28 and aswitch 30,' and avsecond .kggwarp switch or electrically heated time element, 32including aheating coil 34 anda plurality of switches 36 and 38 operatedthereby.` Thereis in the secondary circuit of the transformerrelay I4 aresistance coil 40, the purpose'of whichwill also shown the burnervmotor 6;`the conventional f to one of the switches zo perated by thetrans' systemis' deenergiced`,a n v l areI closedfbutthe''-:llresting*element` 34A is-heated` lforthewhole-period-that'the-motor Gis in oper;y 'u

The main warp switch 30 is connected directly to the line 4 and theopposite side is connected to its own heating element 28, the oppositeside of the heating element being connected by line 42 to the primary I6of the transformer relay I4. v5. The opposite side of the primary I6 isconnected by a line 44 back to the incoming line 2. Line 4 is alsoconnected directly to switchiil,` the opposite side of which isconnected ,by line 46 to the burner motor 6 which is also connected 10 fto the line 2 by a further line 48. Also connected to line 46 is abranch 50 which is connected both to the heating element 34 and oneswitch 36 of the group operated by the warp switch designated at 32. Theopposite side of the heating coil 34 is connected back through line 52to incoming line 2 and the opposite side of the switch 36 is directlyconnected to the primary of the ignition transformer 24 which is thendirectly connected to line v2. The secondary of the ignition transformerof course is connected to a pair of spaced contacts which provide sparksfor ignition purposes. This concludes the high voltage side of thesystem and the secondary or low voltage side will nextbe described.A n25 One terminal ofthe transformer relay secondary AI8 is connectedthrough line 54 to one side of theroomtliermostat I2 which has itsoppositesidel connected toa switch 56 controlled by the stack switch andnormally closed when cold.

y Also inbranchcircuitto onefterminal of the resistance also connectedto switchil is 'a' line opposite end of the resistance 40. A line 62connects the opposite terminal of the resistance 40 former relaywhich'is then extended up to the 40 same terminal of the secondary I 8Vas that t which line 60 is attached. s I, v The warp switch 30 isnormallyclosedunder all conditions andy isyonly' opened; when some ab-45 normal safety condition requires V,itvto do so., The roomthermostat'v is ofl fcourseopened whenk the f temperature of .theroorriis's atbovea certain predetermined level and Vclosed.` as thetemperature falls belowthatjleveh@ The stackvswit'ch 8g-isu closedIwhencold andmopefnsJ-uponan application switches `is andati .I v

'der normal conditions.

former and the magnetic iieldofv thesame will increase appreciably whichcauses a'closing ofthe two switches 28 and 22. The' closing of switch 22i closes an obvious 4circuit to the vburner motor 8` and at the f sametime a parallel circuit through the-heating coil 34, the ignitiontransformer 24 V and switch 38.

Under-these conditions .the burner motor will of course start todischarge a combustible mixture into the chamber andthe ignition willbepresent to/ignite this mixture. The heating ele-- ment 34 however willtend to cause the switch 38 to operi after a predetermined intervalwhich cuts off the ignition andthe burner. thereafter continues tofunction normally. The closure of switch 28 closes a shunt circuitaround the warp switch 38. This however acts to complete the secondarywhen 38 opens due to the heat of the warp switch which willl be actuatedat the samefore continueto operate until a sufficient amount of heat hasbeen provided and when the roomj thermostat opens the whole system -willreturn to its normal deenergized condition.

If,` for example, for some reason the flame does notignite when thermotor startstthe switch 58 will remain closed and the secondary of thetransformer relay will continue to absorb a comparatively large a'mountof current which will of course necessitate a comparatively heavycurrent flowthrough the primary I8 and the heating coil 28 which will,after a predetermined time, cause the safety switch 38 to open and thewhole system will then be deenergized. vThe safety switch 38, as in mostconventional switches of this type, requires a manual resetting after itis once opened. Likewise, if the burner has been operating normally andfor some reason the flame is extinguished momentarily, the stacktemperature will begin to descend and switch v58 will close which will,as before, require a heavy current flow through the secondaryandthereforethe primary-of the transformer I4 and the heating coil 28 ofWarp switch 28 will lagain cause safety switch 38 to open; If, duringnormal operation, the current isvcaused to cease for a short period oftime, the switches 28 and 22 will open. At such time, however, the stackswitch 58, as well as switch 38, is open, and if the current returns to*throw oil or the combustible mixture intothe furnace. Under theseconditions', the switchl I8 is provided to be operated jointly with theignithebbuner without ignition such as might occur, for instance', ifsuch switch 38were not provided and the stack switch 58 returned to itscold closed-position prior to closing of the ignition switch 38 bycooling of the heating coil 34.

The system shown in Figure 2 is a modification of that shown in Figure,1. In this instance the transformer relay I4 is connected to the mainwarp switch 28 in exactly the same way and it operates its rtwo switches28 and 22 in the same manner asbefore. The' warp switch 82 is however,altered as shown a't`32- and a heating coil 84 operates fa' switch 88which controls the ignition transformer 24. The resistance '48 stillshunts the switch 58 operated by the stack switch 8. The. maindifference is that the warp switch 32 has in this instance only onecontact, namely f that for operating the ignition transformer and doesnot control the circuit through the stack tion switch 38 to positivelyprevent starting of' switch which'is in shunt with the controlresistlance 48. The normal operation ofthis vcircuit is substantiallythe same as shown in Figure -1 vfor upon closure of vthe room thermostatI2 the secondary I8 of the transformer relay is energized which draws'current from the primary and causes the closure '-ofthe two switches 28and 22, the firstv completing the circuit through the shunt resistance48 and the second completing Y, thev circuit for the second warp switch,the ignition and motor.

As before, when the stack switch opens the current through the secondaryI8 is cut down due to the series relation of the resistance 48, butthereis suflicient magnetic force to maintain the switches- 28 and 22 closed.When a suilicient ,amount of heat has been provided the room thermostatopens to deenergize the whole sys-v tem.v As far as the safety featuresare concerned,

that shown in Figure 1, with the exception that since there is no switchin series with the stack switch and operated jointly with the ignitionswitch,'as provided in Figure 1 by switch 38, it

' this system operates substantially the'same as is necessary t'osoconstruct the warp switch'32 for the ignition switch 88 that in theevent of a momentary current failure such ignition switch will be closedby cooling of the heating coil 84 before the stack switchv 58 closes oncooling of the stack to prevent starting of the burner motor withoutignition. v

The system disclosed in Figure 3 has a slightly different variation inthat in this case the second warp switch 32 of Figure 1 or 32'v ofFigure 2 is eliminated entirely and the warp switch 28 in this instanceis provided with an extra switch 88 which controls the ignitiontransformer 24. The circuit is otherwise the same as that shown inFigure 2. It should -be pointed out however that in this construction itis necessary to design the two switches 38 and 88 in such a manner lthatthey will operate at different times; in other words, a certain amountof'heat is necessary to operate ignitionswitch 88 to open position butat this time safety switch 38` will still remain closed and it willrequire a substantial increase in the amount of heat supplied before theswitch 38 will open so that under normal running conditions of theburner the ignition switch 88 will be opened soon after starting theburner and the safety switch 38 remain closed. This canbe done of courseby merely designing the bimetal switch 'armeno burner circuit, atransformer, a warp switch and,

actuating element so that this result can be obtained. I

The operation in this case is exactly the same whereby the closure ofroom thermostat I2 will, through the closed stack switch 50, completethe secondary circuit of the transformer relay I4 which will then causethe two switches and 22 to close and the motor 8 and ignitiontransformer 24 will be energized through the closed switches 3l and 58.After a predetermined time, switch 6B will open cutting off theignition, but as before mentioned safety switch is so designed as toremain closed fora longer period and before this time has elapsed switch56 should open due to actuation of the stack switch However the amountof current drawn by the secondary after 56 opens because oftheresistance 40 is enough to maintain a suilicient amount of heat by`coil28 in the primary to keep the switch 58 open as long as the burneroperates. In this case of course if the burner does not ignite, safetyswitch 30 will eventually open deenergizing the whole system, or if theame is extinguished for any reason switch 56 will close after a shortinterval due to the cooling down of the stack and this will again causeswitch 30 to open. If the current fails, contacts 20 and 22 lwill `openand the secondary cannot again be energized until the switch 56 isclosed by cooling of the stack which will allow a purging time for thefurnace. y

I claim:

' l. In a system for controlling huid fuel burners, a burner circuit, anelectrically heated safety switch controlling said burner circuit, aheating element for said switch in series therewith, a transformerhaving its primary in series therewith, a secondary circuit for vthetransformer and means in the secondary circuit and actuated bytemperature changes of the burner to vary the lflow of currenttherethrough which causes a variation of current flow in the primaryandsaid heating element to control the actuation of the safety switchthereby.

2. In a control system for fluid fuel burners,

a burner circuit, an electrically heated safety;

switch controlling said burner circuit, a heating element for saidswitch in series therewith, normally maintained energized atall times, atransformer primary winding in series therewith and with a source ofpower, a secondary transformer winding in inductive relationship to thefirst',

a resistance in series with the secondary circuit,

a shunt circuit around the resistance and means actuated by temperaturechanges of the burner to apply or remove the shunt thereby varying thecurrent in the secondary which reflects back into the primary andaffects the operationy of the safety switch by said heating element.

3. In a control system for fluid fuel burners,

a motor for discharging combustible mixture into the burner, a switchfor controlling motor operation, a transformer having windings locatedin juxtaposition to the switch so that the magnetic field will operatethe same, an electrically heated safety switch in series'with one of thewindings, a heating element for said safety switch in series therewith,a resistance in serieswith the other winding and means actuated bytemperature changes in the burner to shunt the resistance whereby the owof current may be varied in that winding which reect's a change in Aflowin the other winding and in the operation of the safety switch by saidheating element.

4. In a control system for fluid fuel burners, a j

a heating element for said switch in series with the transformer primaryand normally having the transformer no-load current flowing therethroughat all times, said switch controlling the burner circuit, a transformersecondary, a thermostat and a stack operated switch in series with thesecondary to cause a high current to flow, -and a resistance in shunt tothe stack switch and limiting the secondary current when the stackswitch opens.

5. In a control system for fluid fuel burners, a source of current, atransformer relay having a primary and secondary winding, the primarywinding being connected to'the source, an electrically heated warpswitch and a heating element for said switch connected in series withthe primary and normally in circuit at all times, a burner circuitcontrolled by said warp switch, a thermostat, a resistance, both inseries with the secondary winding, a shunt circuit around theresistance, switching means'in the shunt circuit and means responsive totemperature changes of the burner connected to and operating theswitching means whereby burner temperatures.

winding being connected to the source, an electrically heated Warpswitch and a heating element for said switch connected in series withthe primary and normally in circuit at all times, a thermostat, aresistance, both in series with Athe secondary winding, a shunt circuitaround the resistance, switching means in the shunt circuit, meansresponsive to temperature changes of the burner connected to andoperating the switching means whereby burner temperatures will alter thesecondarycurrent and reflect through the transformer to vary the primarycurrent and operate the warp switch, a motor for discharging fuel intothe burner and switching means for the motor operated by the transformerrelay whereby as the current is reduced when the resistance is includedin the secondary the flux of the transformer will maintain the motorswitch closed but will be unable to close it.

7. In a system for controlling fluid fuel burners, a burner motorcircuit, an ignition circuit,

an electrically heated safety switch controlling said circuits, aheating element for said switch in series therewith, a transformerhaving its primary in series with said switch and heating element, asecondary circuit for the transformer,

means in the secondary circuit actuated by temperature changes of theburner to vary the ow of current in the secondary circuit to cause avariation of current flow in the primary and thereby control theactuation of said safety switch by said heating element, a burner motorswitch in said motor circuit, means including a thermostat in thesecondary circuit to control said motor switch,v an ignition switch insaid ignition circuit, athermal time element for operating said ignitionswitch, and a switch in the l secondary in series withv said thermostatand operated by said thermal time element to prevent closure of theburner motor circuit unless lthe ignition circuit is also closed.

8. In'a system for controlling fluid fuel burnondary windings, a burnermotor circuit, an ig- 1| nition circuit, an electrically heated safetyswitch `said relay switch, a thermal time element concontrolling saidcircuits, a heating element for said safety switch in series therewithand in series with the primary winding, a thermostat and a resistance inseries with the secondary winding,

a shunt circuit around the resistance, a switch in said shunt circuit,means responsive to burner temperature connected toand operating saidswitch, a relay switch in said burner circuit,

mA means including said thermostat for controlling trolied by said relayswitch, a normally closed ignition switch'in said ignition circuitoperated by said thermal time element, and a switch in the secondary inseries with said thermostat and secondary winding, said switch beingalso operated by said thermal timeelement to thereby prevent closure ofsaid relay switch unless the ignitionl circuit 'is closed by saidignition switch.

' VAUGHN H. HARDY.

